phosphatidic acid (PA) and diacyl-glycerol (DG) are important molecules in the biosynthesis of membrane lipid and signal transduction. The reaction of turning phosphatidic acid into diacyl-glycerol is catalyzed by phosphatidate phosphatases (PAP), including PAP1 and PAP2. PAP1 is believed to be involved in both cytoplasm and membrane while PAP2 is strictly a membrane protein. The PAP2 gene codes for two forms of proteins, PAP2-alpha 1 and PAP2-alpha 2, by alternative splicing (DNA Cell Biol 1998; 17 (4): 377–85).
Presently, there are three isoforms of PAP2, namely PAP2a, PAP2b and PAP2c. Some research on their structure has been done, like the clarification of the site of glycosylation, the transmembrane functional domain and the catalytic site (FEBS Lett 1998 May 8; 427 (2): 188–92).
A 35 KD murine PAP2 and three human PAP2 isoforms, PAP2a, PAP2b and PAP2c, have been found. These enzymes have six transmembrane functional domains. Their catalytic sites have been preliminarily located between the second and the third outside loop. PAP2 belongs to a large group of soluble membrane binding enzymes. It has been proved that PAP2 can dephosphorize substrates such as soluble phosphatidic acid, ceramide-1-phosphate, sphingol-1-phosphate and diacyl-glycerol et al. It is thought that PAP2 has a wide substrate specificity, but this needs more experiments to support. PAP2 is shown to have the ability to regulate the metabolism of lipids derived from glyceryl and sphingolipid (Chem Phys Lipids 1999; 98 (1–2): 119–26).
The main function of phosphatidate phosphatases (PAP) is to dephosphorize phosphatidic acid to diacyl-glycerol and thus regulate the process of glyceryl lipid biosynthesis and cell signal transduction. Phosphatidate phosphatases (PAP) is an important enzyme in the metabolism process of lipids. Its substrates and products (phosphatidic acid and diacyl-glycerol) act as second messengers in signal transduction processes of living organisms. The present inventors found that cell growth, cell morphology and cytoplasm mobility during cell division are abnormal when the PAP coding gene is mutated (Biochem Biophys Res Commun. 1998; 248 (1): 87–92).
Northern result shows that the expression of PAP2 is suppressed in some tumor tissues. This phenomenon is especially striking in tumors from primary digestive tract. Thus it is deduced that PAP2 and the coding gene can be used for treatment of some tumors (DNA Cell Biol 1998; 17 (4): 377–85).
It has also been shown that PAP2 can act as a regulator of male hormone in prostatic cells. Thus PAP2 can be used for the treatment of prostate related diseases such as prostate cancer (J Biol Chem 1998; 273 (8): 4660–5); (Kai., et al. (1997) J. Biol. Chem. 272, 24572–24578).
Other research results show that PAP2 is related to the processes such as germ cell mobility, and cell division of epithelial tissue, and probably plays an important regulatory role in these processes (Biochim Biophys Acta 1997; 1348 (1–2): 56–62).
The present inventors also found that PAP is related to murine obesity. There is, however, no obvious relationship between overproduction of triglycerides and the activity of PAP based on the comparison of PAP activity in the adipose tissue of adiposis patient and normal people (Lipids 1989; 24 (12): 1048–52).
Biopsy studies showed that when compared to normal muscle tissue, the expression of PAP in nutrionally deficient muscle tissue is much lower in microsome while higher in the cytoplasm and mitochondrion (Clin Chim Acta 1985; 146 (2–3): 167–74).
The human polypeptide of the present invention shares 36% identity and 57% similarity at the amino acid sequence level with PAP. They have similar structural characteristics and belong to the same phosphatidate phosphatase protein family, and are believed to have similar biology functions. The polypeptide of the present invention is thus named phosphatidate phosphatase 29.81.
As described above, phosphatidate phosphatase 29.81 plays an essential role in the regulation of important biological functions such as cell division and embryogenesis, and it is believed that many proteins are involved in these regulations. So the determination of those related phosphatidic acid phosphatase 29.81, especially of their amino acid sequences is always desired in this field. The isolation of this novel phosphatidic acid phosphatase 29.81 forms the basis for research of the protein function under normal and clinical conditions, and this protein can be used in disease diagnosis and/or drug development.